This invention relates to injection devices.
It concerns devices which are fitted with a syringe having a capsule with a needle projecting from the forward end and a plunger from the rear end. A trigger and spring mechanism, when operated, shoots the syringe forwardly to project the needle, and then continues to act on the plunger to eject the dose. There is also a return spring arrangement to retract the needle after use, thereby making it safe.
Hitherto, these firing devices have been quite complicated and expensive, and it is necessary to load and unload the syringe before and after use and to keep the device itself for repeated use. It is too expensive simply to throw away. Also there have been problems with ensuring that the return spring works properly.
However, unloading particularly has its dangers with a sharp and possibly contaminated needle, and it is the aim of this invention to provide an injection device which is simple and cheap enough to be thrown away with the syringe safely retracted inside it.